The importance of determining a fossil-fired power plant""s or steam generation system""s heat rate (inversely related to thermal efficiency) is critical if practical day-to-day improvements in heat rate are to be made, and/or problems in thermally degraded equipment are to be found and corrected. Although elaborate analytical tools are sometimes needed, simpler and less expensive methods are also applicable which do not require high maintenance nor the input of complex operational system data, and, also, whose accuracy is not greatly compromised. The L Factor method addresses this need.
General background of this invention is discussed at length in application Ser. No. 09/273,711 (hereinafter denoted as ""711), and in application Ser. No. 09/047,198 (hereinafter denoted as ""198). In ""711 the L Factor is termed the xe2x80x9cfuel factorxe2x80x9d.
As discussed in ""711, related art to the present invention was developed by Roughton in 1980; see J. E. Roughton, xe2x80x9cA Proposed On-Line Efficiency Method for Pulverized-Coal-Fired Boilersxe2x80x9d, Journal of the Institute of Energy, Vol.20, March 1980, pages 20-24. His approach using the L Factor (termed Md/Id in his work) in developing boiler efficiency was to compute system losses such that xcex7Boiler=1.0xe2x88x92xcexa3(System Losses). This is a version of the Heat Loss Method discussed in ""711. The principle losses he considered were associated with dry total effluents (termed stack losses), effluent moisture loss and unburned carbon loss. Roughton""s method produces boiler efficiency independent of any measured fuel flow and independent of any measured total effluents flow.
Related art known to the inventor since ""711 and ""198 were filed is the technical paper: S. S. Munukutla, xe2x80x9cHeat Rate Monitoring Options for Coal-Fired Power Plantsxe2x80x9d, Proceedings of Heat Rate Improvement Conference, Baltimore, Md., sponsored by Electric Power Research Institute, September 1998. In this paper Munukutla explains 40 CFR Part 60, Appendix A, Method 19, and the use of its F Factor to determine heat rate. Munukutla makes no mention of correction factors, neither conceptual nor those associated with measurement error. He concludes xe2x80x9c. . . that the heat rate, as determined by the F-factor method, is in error by at least 10-20%.xe2x80x9d In his xe2x80x9cConclusionsxe2x80x9d section, Munukutla states that: xe2x80x9cThe F Factor method may give accurate results, provided the stack gas flow rate and CO2 concentration can be measured accurately.xe2x80x9d He makes no mention of the molecular weight, or assumed composition, of the total effluents from combustion. Further, Munukutla explicitly states in his writing and by equation that system heat rate is inversely proportional to the concentration of effluent CO2.
Other related art is the technical presentation by N. Sarunac, C. E. Romero and E. K. Levy entitled xe2x80x9cF-Factor Method for Heat Rate Measurement and its Characteristicsxe2x80x9d, presented at the Electric Power Research Institute""s (EPRI) Twelfth Heat Rate Improvement Conference, Jan. 30 to Feb. 1, 2001, Dallas, Tex. and available from the proceedings (EPRI, Palo Alto, Calif.). This work discusses the CO2 based FC Factor and the O2 based FD Factor and their use in determining system heat rate. They stated that the F Factor method is not used due to its low precision and accuracy, siting 5 to 25% error compared to conventional heat rate methods. The authors site the principal sources of error as being the flue gas flow rate, and either the CO2 concentration or the O2 concentration measurement in the effluent. They discuss methods of improving the measurement accuracy of these quantities. These authors also indicate by equation that heat rate is inversely proportional to the concentration of effluent CO2 or O2.
Related art to the present invention also includes the EPA""s F Factor method, discussed in ""711, and whose procedures are specified in Chapter 40 of the Code of Federal Regulations (40 CFR), Part 60, Appendix A, Method 19. Assumed by Method 19 is that an FC, FD or FW Factor is the ratio of a gas volume (of CO2 or O2) found in the combustion products to the heat content of the fuel.
The monitoring of a fossil-fired system may involve detailed and complete descriptive understanding of the fuel being burned, analyses of all major components, and accurate determination of its fuel flow. Such monitoring is possible by applying the Input/Loss Method discussed in ""711 and ""198. However, for many fossil-fired systems simpler methods are needed which allow the installation of analytical tools which provide an inexpensive, but consistent, indication of a system""s thermal performance. From such indication, the system""s efficiency may be monitored, deviations found, and corrections implemented. This invention discloses such a tool. Its accuracy is not at the level of the Input/Loss Method, but has been found to be within 1% to 2% when monitoring on-line, and, as importantly, has been demonstrated to be consistent.
This invention employs an L Factor to determine system heat rate. A heat rate may also be computed using the EPA""s F Factor, but with additional error relative to the L Factor, but which may be tolerable. The L Factor and the F Factor may be used to determine heat rate only if certain correction factors are applied as taught by this invention. These correction factors are both conceptual and for routine measurement error.
The present invention, termed the L Factor Method, determines total fuel energy flow of a fossil-fired system resulting, when the total fuel energy flow is divided by the measured system electrical output, the heat rate of the system. Acceptable heat rate accuracy is achievable through the demonstrated high consistency found in the L Factor, to which this invention makes unique advantage.
The L Factor method does not use any part of the Heat Loss Method, it does not compute nor need any thermal loss term as used by Roughton. Unlike Roughton""s method, the L Factor method employs the principle effluent flow or fuel flow associated with a fossil-fired system.
This invention is unlike the works of Munukutla and Sarunac, et al, several key areas. First, as taught by this invention, system heat rate using the F Factor is directly proportional to the concentration of effluent CO2, not inversely proportional as stated by these authors. Further, this effluent CO2 is associated with theoretical combustion, not actual combustion as these authors believe. Further, it has occurred during the development of this invention that certain conceptual correction factors must be applied to the L Factor to correctly and accurately monitor a fossil-fired system. No corrections of any kind are mentioned by these authors. This is significant to this invention for the F Factor affords one method of computing the L Factor (there is another which is preferred), however conceptual corrections which have been found to apply to the L Factor, also fundamentally apply to the F Factor. And lastly, these authors make no mention of the molecular weight, or alternatively the assumed composition, or alternatively the density of the total effluents being produced which this invention teaches must be addressed as different fossil fuels produce different mixes of combustion products comprising the total effluents.
In the process leading to the present invention, several problems existing with the F Factor concept have been both clarified and solutions found. These problems include the following: 1) large conventionally fired power plants have air in-leakage which alters the total effluents concentration""s average molecular weight from base assumptions; 2) different Ranks of coal will produce different effluent concentrations thus different average molecular weights from base assumptions; 3) circulating fluidized bed boilers are injected with limestone to control SO2, limestone produces CO2 not addressed by the FC Factor; 4) many poor quality coals found in eastern Europe and from the Powder River Basin in the United States may have significant natural limestone in its fuel""s mineral matter, thus producing effluent CO2 not addressed by the FC Factor; 5) the EPA requires the reporting of emission rates based on measured wet volumetric flow reduced to standard conditions, but the quantity of effluent moisture is not independently measured, whose specific volume varies greatly as a function of its molar fraction thus introducing a major source of error in using volumetric flow; and 6) ideal gas behavior is assumed.